1. Field of the Invention
The present invention relates to a fluid fan clutch device of a type in which fan rotation for engine cooling generally in an automobile or the like is controlled according to a change in external ambient temperature or rotation and, in more detail, relates to a highly reactive fluid fan clutch device for improving quickness of reaction of fan rotation to a control signal.
2. Description of the Related Art
Conventionally, as a fan clutch device for controlling fan rotation for engine cooling in an automobile or the like to supply an amount of cooling blast to the engine, there are a temperature-sensitive type, an external control type, and the like. The temperature-sensitive type includes an example of a fan clutch in which: the inside of a sealed housing composed of a case and a cover is partitioned into an oil reserving chamber and a torque transmission chamber that has a drive disk incorporated therein, by a partition plate having an oil supply adjusting hole; a dam for collecting and reserving oil during fan rotation is provided on a part of an inner circumferential wall on a side of the sealed housing facing an outer circumferential wall part of the drive disk; an oil circulating flow passage continuing from the dam is provided between the torque transmission chamber and the oil reserving chamber; a valve member is included inside, the valve member opening the supply adjusting hole of the partition plate when the temperature of external ambient or the like exceeds a set value and closing the supply adjusting hole of the partition plate when the temperature is equal to or lower than the set value; and an effective contact area of oil in a torque transmission gap provided between the drive disk and an opposite wall face near the outside of the sealed housing is increased/decreased to control torque transmission from a drive side toward the sealed housing on a driven side. A fan clutch device of this type generally detects an atmospheric temperature using a bimetallic strip or a bimetallic coil, thereby adjusting the opening degree of the oil supply adjusting hole according to the detected value (see Japanese Patent Publication No. S63-21048). For the external control type, while the basic structure thereof is similar to that of the temperature-sensitive fan clutch device, a valve member for opening and closing the oil supply adjusting hole of the partition plate is made of a magnetic material, and the magnetic valve member is controlled by an electromagnet provided externally. An example of this structure is such that a pair of electromagnets are provided on a front or rear face side of the sealed housing and the magnetic valve member for opening and closing the oil supply adjusting hole of the partition plate is provided opposite the electromagnets (see Japanese Patent Publication No. S63-21048).
Furthermore, a viscous friction clutch of an external control type for driving a cooling fan of a vehicle has been known. The viscous friction clutch is characterized by, for example, including: a drive disk and a housing (a case and a cover); an annular supply chamber and a working chamber; and a device for supplying a shear fluid (oil) from the supply chamber into the working chamber and a device for returning the shear fluid from the working chamber to the supply chamber, part of the supply chamber including a storage chamber for the shear fluid, the storage chamber being separated from the working chamber by another part of the supply chamber, the supply chamber being provided inside the housing, the storage chamber comprising an annular segment formed as a supplementary receptacle, the supply chamber including at least one supply bore and at least one return bore (collection port), and the supply and return bores forming part of the devices for supplying and returning the shear fluid. In the external control type fan clutch device having these configuration, viscous oil flowing out from the supply bore on the case or cover side of the housing is supplied to torque transmission units (labyrinth units) provided on the drive disk and the case and the cover of the housing due to a centrifugal force occurred during fan clutch rotation.
In the conventional fan clutch devices disclosed in Japanese Patent Publication No. S63-21048 and Japanese Patent Application Laid-Open No. 2002-81466, the oil supply adjusting hole that the valve member opens and closes is provided on the driven side because of the configuration where the drive torque of the drive disk is transferred to the sealed housing (case) by the oil supplied from the oil reserving chamber to the torque transmission chamber through the oil supply adjusting hole of the partition plate and thereby rotating a fan mounted on the sealed housing. Thus, the conventional fluid fan clutch device of this type has a disadvantage that the centrifugal force during low fan rotation (OFF rotation) is weak and the supply amount of oil is decreased accordingly, which leads to slow reaction when the fan rotation increases, and at a result, it disadvantageously takes time to rotate the fan at high speed. Moreover, for a snowplow (a vehicle with a moldboard for snowplowing provided in front of a front grille), air velocity on the front face of the front grille is slower than its peripheral air velocity, and then a difference in pressure occurs between the inside of the engine room and the periphery of the front grille, or the flow of wind in a direction opposite to the fan occurs by swirled-up wind from under the floor. With this, rotation of the fan becomes significantly decreased, thereby disadvantageously slowing down or inhibiting the reaction when the fan rotation increases to prevent an increase in rotation of the fan to cause overheat.
Still further, a fluid fan clutch device of an external control type has been known in which viscous oil flowing out from the supply bore on a case or cover side of a housing is supplied to a torque transmission units (labyrinth units) provided on a drive disk and the case and the cover of the housing due to the centrifugal force occurred during fan clutch rotation. Since this type of fluid fan clutch device has the supply bore on the driven side, the centrifugal force becomes weaker at the time of low fan rotation (OFF rotation), and the supply of the viscous oil also becomes weak accordingly, thereby disadvantageously causing slow reaction of fan rotation to a control signal.